get yourself a piano or a keyboard. memorize middle c, and become really good at recognizing intervals.

In my opinion, this is not a very good approach, as it requires a cognitive process for each tone one wish to identify. It's far better to learn to identify tone by how they sound, without using relative pitch.

As user "caddywumpus" wrote, one can obtain perfect pitch. I'm in the process of developing this ability as we speak, and can clearly hear how tones on my guitar (I'm a guitarist) and on the piano are as different as visual colors are. It's not very difficult at all, but one need to understand the concept. I recommend David L. Burge's "Perfect Pitch" ear training course to get the knowledge, and apply this knowledge to work on ones "color hearing" ability.